It's my first topic here and I spent the day searching on the web for it: I have 2 Arduinos (Seeduino R3 and Arduino Leonardo) that needs to be connected together via I2C but at the same time both via USB serial to the computer. And I never have seen such a thing.

My questions are:

1. Will it work, since both need to share the 5V and GND and both are with their own power supply (via USB)? I didn't try it just because I think it can harm the boards.

2. I tried to just connect the two cables for SCL and SDA without the 5V and GND and it all went fine when running the wire lib skecthes. Will it work on a long run or with a more complex program? Could this damage my Arduinos in anyway?

1. Will it work, since both need to share the 5V and GND and both are with their own power supply (via USB)? I didn't try it just because it think it can harm the boards.

The only other connection needed (besides the SDA and SCL lines) is GND. There's no need to connect the 5V.

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2. I tried to just connect the two cables for SCL and SDA without the 5V and GND and it all went fine when running the wire lib skecthes. Will it work on a long run or with a more complex program? Could this damage my Arduinos in anyway?

That probably worked because you're using the same computer for the two Arduinos. That way they already share a common ground (over the USB connection). Just because of this you cannot damage your Arduinos.

The only other connection needed (besides the SDA and SCL lines) is GND. There's no need to connect the 5V.

OK, I will try it!

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That probably worked because you're using the same computer for the two Arduinos. That way they already share a common ground (over the USB connection). Just because of this you cannot damage your Arduinos.

Good to know. I usually use my Mac Pro connected to my Leonardo and PowerBook to the other when coding, just to don't have to be switching between ports and boards on the Arduino app. Luckly, this time, I was too lazy to turn on the PowerBook and did all in the Mac Pro. I'll be on the safe side next time and ground both together...

I understand that this works with only 2 devices connected. More than this I'll need pull-up resistors connecting SDA and SCL to the 5V. I'm planning, in this setup, to add a I2C RTC to the Leonardo. So, will I need to make a pull-up from the Leonardo's 5V, anyone or neither? Or this setup won't work at all?

Would you mind to share your source of information? I want to learn more about I2C from a complete source (I went crazy yesterday seeking for this information).

I understand that this works with only 2 devices connected. More than this I'll need pull-up resistors connecting SDA and SCL to the 5V. I'm planning, in this setup, to add a I2C RTC to the Leonardo. So, will I need to make a pull-up from the Leonardo's 5V, anyone or neither? Or this setup won't work at all?

This works up to over 100 devices connected together (theoretically). You need pull-ups once per bus (again theoretically, for a few devices and a short bus this is correct). Adding the RTC should be no problem, just connect GND, SDA, SCL and Vcc (to power the RTC).

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Would you mind to share your source of information? I want to learn more about I2C from a complete source (I went crazy yesterday seeking for this information).

There wasn't one single source of information, you get some experience if you work with it and read the forum .

I've just realised that to have the system working all the time, I will need to have, besides the 2 USB cables for serial communication, 2 power supplies (for when the computer is disconnected). There's anyway that I could use only one PS, say, for the Seeeduino R3, but keeping the features discussed above? (2 USB cables and I2C connection between both and the RTC)

If not, can the Leonardo "login the network" as a slave at anytime, i.e., when the computer starts and be recognized?

I need the Leonardo only to send my Mac keystrokes and shortcuts, for automation with Keyboard Maestro. I wouldn't need one more Arduino unless the EasyVR Shield were compatible with Leonardo. But also it would be great to have the IRRemote and VirtualWire libs running on different Arduinos, since they are incompatible (I think it has something to do with timers) and the workaround was to substitute VirtualWire with MANCHESTER for RF communications (yeah, I have anothers Arduinos receiving commands), which is far inferior than VW.

I've just realised that to have the system working all the time, I will need to have, besides the 2 USB cables for serial communication, 2 power supplies (for when the computer is disconnected). There's anyway that I could use only one PS, say, for the Seeeduino R3, but keeping the features discussed above? (2 USB cables and I2C connection between both and the RTC)

If you supply one Arduino, you can just connect the other with GND and 5V pins (on both MCs) and you have power for both. This works if the second Arduino doesn't pull too much power (the RTC is absolutely no problem).

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If not, can the Leonardo "login the network" as a slave at anytime, i.e., when the computer starts and be recognized?

To wich network? In the previous posts you haven't had any network equipment involved. And what does "slave" mean in this context?

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I wouldn't need one more Arduino unless the EasyVR Shield were compatible with Leonardo.

Unfortunately there doesn't seem to be any documentation about that shield. The library is fully compatible with the Leonardo, my guess is, the shield is too. At least I couldn't find any specification that would rule against that. Do you have a schematic of the shield (I couldn't find one)? The EasyVR module is completely compatible with the Arduino Leonardo. If the shield isn't done too badly it should be as well.

If you supply one Arduino, you can just connect the other with GND and 5V pins (on both MCs) and you have power for both. This works if the second Arduino doesn't pull too much power (the RTC is absolutely no problem).

Sharing the 5V between them with USB cables connected to both? Could it be done? Is there some kind of protection as it has when you connect both USB and power supply?

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To wich network? In the previous posts you haven't had any network equipment involved. And what does "slave" mean in this context?

I'm sorry, I didn't know how to name it, I meant the I2C "network"...

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Unfortunately there doesn't seem to be any documentation about that shield. The library is fully compatible with the Leonardo, my guess is, the shield is too. At least I couldn't find any specification that would rule against that. Do you have a schematic of the shield (I couldn't find one)? The EasyVR module is completely compatible with the Arduino Leonardo. If the shield isn't done too badly it should be as well.

As I said on the original post for the EasyVR Shield problem: I changed the pins to 8/9 instead of 12/13 and while normal operation it works fine (with some few bugs). But Leonardo can't operate as a brigde between the Shield and the EasyVR Commander app (used to upload, voice commands to the module). Neither in PC mode (there are jumpers in the shield to choose which mode to use), used to upload soundtables, as it was expected, since the Arduino is held in reset just to interface the module thru the USB serial using the default pins (12/13).

The official answer to this question via email is that:

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the leonardo has differences in the pinout.Please check the following pages where the differences are.

which didn't get me very far, since there are no explanations about the pin diferences, only that Leo uses Serial1 instead of Serial to connect... I already tried changing on the libs, but without any changes.

Sharing the 5V between them with USB cables connected to both? Could it be done? Is there some kind of protection as it has when you connect both USB and power supply?

If the USB connection goes to the same computer you shouldn't have a problem. Else disconnect the 5V connection between the two Arduinos if you connect the other USB line.

I2C is not a network, it's a bus. And a slave cannot "login" to that bus, it just listens on the bus for commands from the master and replies if it's instructed to do so.

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But Leonardo can't operate as a brigde between the Shield and the EasyVR Commander app (used to upload, voice commands to the module). Neither in PC mode (there are jumpers in the shield to choose which mode to use), used to upload soundtables, as it was expected, since the Arduino is held in reset just to interface the module thru the USB serial using the default pins (12/13).

That's something completely different. It seems that the PC mode just connects the serial interface of the EasyVR module to the pins 0 and 1 of the Arduino. Because the Leonardo has a completely different way of communicating with the PC over USB, this doesn't work out of the box. Do you know a what baudrate theat EasyVR Commander is communicating with the module?

To help you further with this stuff, I need the schematics of the EasyVR shield. If I don't know how this stuff is interconnected I'm always guessing and that's more than boring. Provide a link to the schematics of that shield.

The initial configuration at power on is 9600 baud, 8 bit data, No parity, 1 bit stop. The baud rate can be changed later to operate in the range 9600 - 115200 baud.

When in PC mode, from the manual, again:

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The full speed used is 230400 bit/s, but the option "Slow transfer" can be used to reduce it to 115200, for better compatibility with slower serial adapters2. One adapter that can go to full speed is the SmartVR DevBoard. Otherwise any USB/Serial adapter with TTL/CMOS interface can be used for updating the flash. The EasyVR Shield can be used for the download, provided that the jumper (J12) is in UP position.

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To help you further with this stuff, I need the schematics of the EasyVR shield.

I asked the support guy via email for this, let's see what he replies!

This is just copying data from the USB to the hardware serial and vice versa. Configure the jumper for hardware serial, also during the EasyVR Commander session.

The only problem that may still exist is the RST line. It's connected to the RESET line of the Arduino. If the EasyVR Commander controls that line via the DTR of the serial interface, I don't have a solution for that shield. Then it's probably easier to just buy a standard UNO for this shield.

I'll try it! But I think that this means that I'll have to connect pins 0 and 1 from both together (the shield is now only connected via RST, GND, 5V pins 12 to 8 and 13 to 9 to the arduino). No biggie... jumper wires for the job!

Later I tell you what happened...

Edit: It didn't work as well...

But I'm resigned. No big deal. I can always change it with the seeeduino everytime I want to update the soundtable or voice commands...

Thank for your willing to help all the time! I learned so much from here and the manuals!